The present invention relates to a mobile communication system and more particularly to a mobile communication system allowing communication to be held on a portable telephone or similar mobile terminal moved from one network to another network, and a mobile communication method.
The spread of PHS (Personal Handy-Phone system) and other portable telephone systems has derived a convenient mobile communication environment. A portable telephone is usable anywhere in an office as an extension telephone and allows a person carrying it to be located on the basis of a location display function available therewith. Further, a person carrying a portable telephone can use it for a private purpose outside of an office via a general telephone channel.
In a relatively small office, all the portable telephones registered at a network constructed in the office can be dealt with by a single exchange. However, in a relatively large office or a company or organization having a plurality of offices distributed in, e.g., an urban area, it is impossible for a single exchange to manage all the portable telephones in the geographical or capacity aspect. In light of this, there has been proposed a system in which a plurality of exchanges are distributed in a preselected area, and each manages particular portable telephones. In this system, when a person carrying a portable telephone moves from, e.g., one building to another building owned by the same company or organization, the above proposed system manages the telephone as if the telephone were connected to a single exchange. Such control over communication is achievable because a plurality of exchanges constitute an apparent, single exchange system.
In practices however, the possibility that a mobile telephone is moved between different networks must be taken into account. For example, if a mobile telephone moved from a first network to a second network is dealt with as a visitor terminal, a call can be originated on the mobile telephone. However, when a call is originated on the mobile telephone registered at the first network, but moved to the second network, hand-over is cannot be executed if the telephone in communication enters another area of the second network.
Japanese Patent Laid-Open Publication No. 8-65236 discloses a system that implements radio mobile communication without regard to the position of a mobile telephone as well as hand-over between a plurality of telephone-based radio networks. The system, however, pertains to radio mobile communication using exchanges that are connected to the same network. That is, the system does not work when a mobile telephone or visitor terminal moved from a first network to a second network further moves between exchanges connected to the second network.
Technologies relating to the present invention are also disclosed in Japanese Patent Laid-open Publication Nos. 8-237727, 10-4581, 11-122659 and 11-298930 and Japanese Patent NO. 2,970,603.
It is an object of the present invention to provide a mobile communication system and a mobile communication method capable of implementing, when a mobile terminal registered at a first network enters a second network including a plurality of exchanges and starts communication, hand-over between the exchanges of the second network even if the mobile terminal in communication moves in the second network.
In accordance with the present invention, a mobile communication system includes a network identification information obtaining circuit belonging to a first network for obtaining, when a mobile terminal not registered at the first network enters the first network as a visitor terminal, identification information that identifies a second network at which the mobile terminal is registered. An authentication information requesting circuit requests, based on the identification information obtained, the second network to send authentication information necessary for the visitor terminal to communicate in the first network. When the authentication information is received from the second network, an authentication information storage stores the authentication information in any one of a plurality of exchanges belonging to the first network. A call information storage stores call information generated when the visitor terminal starts communication in the first network. An exchange storage stores information representative of the exchanges each storing the authentication information and call information of a particular visitor terminal. When any one of the exchanges needs for hand-over the authentication information and call information of the visitor terminal that moves while in communication, a searching circuit searches the contents of the exchange storage to thereby locate the exchange storing the authentication information and call information and provides the above one exchange with the authentication information and call information.
A mobile communication method for executing above procedure is also disclosed.